Ground electrode backfill composition, anode bed and apparatus

Abstract

A low resistance non-permeable backfill especially for use in vertical anode beds for cathodic protection of subsurface metallic structures includes a mixture of carbonaceous materials, naturally occurring graphite lubricants, additives to reduce the apparent viscosity of the slurry and portland cement mixed with water and pumped as a high density fluidized suspension into the anode bed, particularly around the casing of a deep anode bed of the general type described in United States patent to Tatum U.S. Pat. No. 3,725,669.

I claim: 
     
       1. A conductive non-porous backfill material for earth anode beds comprising, a mixture of sized calcined fluid petroleum coke, naturally occurrihg graphite flakes, viscosity reducers and portland cement. 
     
     
       2. A conductive non-porous backfill material for earth anode beds comprising a mixture of the following components:   ______________________________________                                    
                  Percent by Weight                                       
                  of Total Mixture                                        
______________________________________                                    
Calcined Fluid Petroleum Coke                                             
                    83.5- 85                                              
Portland Cement     15- 16                                                
Powdered Graphite    .75- 1.25                                            
Surfactant          .25- .5                                               
______________________________________                                    
     
     
     
       3. The backfill material of claim 1 in which said particular calcined fluid petroleum coke is of a size to pass a Tyler Standard number 16 sieve. 
     
     
       4. The conductive non-porous backfill material of claim 1 in which said surfactant is nonionic. 
     
     
       5. In apparatus for cathodically protecting underground metallic structure having an elongated hollow tubular rigid casing for reception within a deep bore hole, said casing having at least an upper portion constructed of substantially rigid chemically inert nonconductive material with a plurality of openings adjacent to the lower end only, at least one anode, means for suspending said anode within said casing in the area of said openings, first granular electrically conductive material within said casing and intimately engaging said anode, and second granular electrically conductive material filling the lower portion of the bore hole exteriorly of said casing at least to a level above said openings, and means for supplying direct electrical energy to said anode, whereby electrical energy flows from said anode through said first and second conductive materials and through the earth to the underground metallic structure to cause the underground structures to become cathodic and thereby substantially prevent corrosion of such structure, the improvement comprising, said second electrically conductive material comprising concrete formed from a hydrated mixture according to any of claims 1, 2, 3 or 4. 
     
     
       6. Apparatus for cathodically protecting underground metallic structures comprising an elongated hollow tubular rigid casing for reception within a deep bore hole, said casing having an upper portion constructed of substantially rigid chemically inert nonconductive material and a lower portion of conductive material, at least one anode, means for suspending said anode within said lower portion of said casing, first granular electrically conductive material within said casing and intimately engaging said anode, and second granular conductive hydrated material according to any of claims 2, 3, 4 or 5 forming a concrete annulus around said lower portion of said casing and filling the lower portion of the bore hole exteriorly of said casing at least to a level above said anode, and means for supplying direct electrical energy to said anode, whereby electrical energy flows from said anode through said first and second conductive material and the lower portion of said casing through the earth to the underground metallic structure to cause the underground structure to become cathodic and thereby substantially prevent corrosion of such structure. 
     
     
       7. In the method of making a deep anode bed for the cathodic protection of underground metallic structures comprising the steps of: drilling a deep bore hole in the earth, inserting an elongated hollow casing having a generally tubular wall of relatively rigid chemically inert non-conductive material into said bore hole, the lower portion of said casing wall having a plurality of openings therethrough, filling the annulus between the bore hole and the exterior of said casing with electrically conductive material to a predetermined level above the bottom of the bore hole and at least above the level of said openings, attaching at least one anode to a support means, introducing said anode and at least a portion of said support means into said casing, filling the interior of said casing with granular electrically conductive material to at least above the level of said openings after said anode is in place so that the conductive material within said casing is in intimate engagement with said anode and communicates with the conductive material exteriorly of said casing through said openings, and electrically connecting said anode to a source of direct electrical energy, whereby electrical energy flows from said anode through said interior and exterior conductive material and through the earth to the metallic structure so that the underground metallic structure becomes cathodic, the improvement comprising filling the annulus between the bore hole and the exterior of said casing with a hydrated mixture according to any of claims 1, 2, 3 or 4 to form an electrically conductive concrete shell around the casing. 
     
     
       8. The method of making a deep anode bed for the cathodic protection of underground metallic structures comprising the steps of: drilling a deep bore hole in the earth, inserting an elongated hollow casing having a generally tubular wall into said bore hole, the upper portion of said casing constructed of substantially rigid inert non-conductive material, the lower portion of said casing formed of substantially rigid conductive material, filling the annulus between the bore hole and the exterior of said casing with a hydrated mixture according to any of claims 1, 2, 3 or 4 to a predetermined level above the bottom of the bore hole substantially commensurate with the lower portion of said casing to form an electrically conductive concrete shell and around the casing, attaching at least one anode to a support means, introducing said anode and at least a portion of said support means into said casing, filling the interior of said casing with granular electrically conductive material after said anode is in place to the extent that the conductive material within said casing is in intimate engagement with said anode and communicates electrically with the conductive shell exteriorly of said casing through said lower portion of said casing, and electrically connecting said anode to a source of direct electrical energy, whereby electrical energy flows from said anode through said interior material and exterior shell and said lower portion of said casing and through the earth to the metallic structure so that the underground metallic structure becomes cathodic.